1. Field of the Invention
The present invention relates to an output stage circuit of a class D amplifier.
2. Description of the Related Art
Heretofore, in the reproduction of audio signals, systems utilizing a class D amplifier in an output stage thereof are widely available. In such a system, for example, after a digital audio signal undergoes delta sigma (AS) modulation, a PWM signal is amplified by a class D amplifier and output to a speaker. In particular, the class D amplifier has good power efficiency and is desirable in portable devices where battery life becomes a problem.
In an output stage of this class D amplifier, output transistors are driven by the PWM signal and a driving current thereof is supplied to a speaker. In particular, in the case of the class D amplifier, since the output transistors are driven by the PWM signal, a coil and a capacitor are inserted between the output transistors and the speaker to smoothen the drive of the speaker.